1. Field of the Invention
This invention relates generally to electronic switches having no moving contacts, and more specifically, to such electronic switches utilizing a switching signal generated by deformation of a piezoelectric material.
2. Description of the Prior Art
Contactless piezoelectric switches are known in the prior art. Typically, such switches employ a deformable face or surface, and a thin body of piezoelectric material arranged such that a deforming force is transmitted from the face or surface to the piezoelectric material, thus causing the material to generate an electrical signal. Electrodes are employed in conjunction with the body of piezoelectric material so that the electrical signal may be communicated to, for example, switch circuitry. Thus, when the deformable face is pressed by the user, the piezoelectric material generates an electrical signal and activates the switching circuit. Such switches are disclosed in, for example, U.S. Pat. Nos. 3,339,104 and 4,618,797.
Such contactless switches have inherent advantages over conventional switches with moving parts in that they can be made vandal-proof and are much less sensitive to environmental degradation. They have no moving parts or electrical contacts to wear out, and produce no electrical arc or electromagnetic interference, a great benefit in explosive or sensitive electronic environments.
However, the piezoelectric contactless switches of the prior art suffer from certain disadvantages. Prior art piezoelectric switches have limited control functions. They are generally limited to simple on and off switching. In addition the sensing of operation of prior art piezoelectric contactless switches tends to be unreliable due to the numerous sources of noise in the signal from the piezoelectric element.
It would be desirable to provide a contactless, piezoelectric switch assembly which can provide a number of switch functions is a reliable manner.